SQL (/ˌɛsˌkjuːˈɛl/ (About this soundlisten) S-Q-L, /ˈsiːkwəl/ "sequel"; Structured Query Language) is a domain-specific language used in programming and designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS). It is particularly useful in handling structured data, i.e. data incorporating relations among entities and variables.
SQL offers two main advantages over older read–write APIs such as ISAM or VSAM. Firstly, it introduced the concept of accessing many records with one single command. Secondly, it eliminates the need to specify how to reach a record, e.g. with or without an index.
Originally based upon relational algebra and tuple relational calculus, SQL consists of many types of statements, which may be informally classed as sublanguages, commonly: a data query language (DQL),[a] a data definition language (DDL),[b] a data control language (DCL), and a data manipulation language (DML).[c] The scope of SQL includes data query, data manipulation (insert, update and delete), data definition (schema creation and modification), and data access control. Although SQL is essentially a declarative language (4GL), it also includes procedural elements.
SQL was one of the first commercial languages to use Edgar F. Codd’s relational model. The model was described in his influential 1970 paper, "A Relational Model of Data for Large Shared Data Banks". Despite not entirely adhering to the relational model as described by Codd, it became the most widely used database language.
SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987. Since then, the standard has been revised to include a larger set of features. Despite the existence of standards, most SQL code requires at least some changes before being ported to different database systems.
Glossop is a market town in the High Peak, Derbyshire, England, 12 miles (19 km) east of Manchester, 24 miles (39 km) northwest of Sheffield and 32 miles (51 km) north of the county town, Matlock, near Derbyshire's borders with Cheshire, Greater Manchester, South Yorkshire and West Yorkshire. It is between 150 and 300 metres (492 and 984 ft) above mean sea level, and lies just outside the Peak District National Park.
Historically, the name Glossop refers to the small hamlet that gave its name to an ancient parish recorded in the Domesday Book of 1086, and then the manor given by William I of England to William Peverel. A municipal borough was created in 1866, and the unparished urban area within two local government wards. The area now known as Glossop approximates to the villages that used to be called Glossopdale, on the lands of the Duke of Norfolk. Originally a centre of wool processing, Glossop rapidly expanded in the late 18th century when it specialised in the production and printing of calico, a coarse cotton, and became a mill town with many chapels and churches, its fortunes tied to the cotton industry.
Architecturally, the area is dominated by buildings constructed of the local sandstone. There remain two significant former cotton mills and the Dinting railway viaduct. Glossop has transport links to Manchester, making the area popular for commuters.